1. Field of the Invention
The present invention relates to a two-dimensional spectroradiometer for acquiring a spectral intensity of each pixel of a two-dimensional light source as an object for measurement, and converting the spectral intensities of the pixels into a two-dimensional distribution of an index such as luminance or chromaticity for output.
2. Description of the Related Art
Heretofore, a two-dimensional tri-stimulus colorimeter using a filter has been used to measure the luminance or chromaticity of a two-dimensional light source. In recent years, use of a surface light source having an emission spectrum approximate to a monochromatic ray, namely, having a narrow spectral bandwidth such as various display devices and LED-applied devices has been increasing, and a need for a two-dimensional spectroradiometer has been increasing in light of a demand for precise measurement of the luminance or chromaticity of such a surface light source. Many of the two-dimensional spectroradiometers are of a multi-filter type or of a type using a dispersed image through a slit, as described below.
<Multi-Filter Type>
According to a luminance measuring system, plural band pass filters (BPF) which have central wavelengths different from each other and are mounted on a rotary disk or a like device circumferentially around a rotational axis thereof are successively placed in an optical path of imaging light rays emanated from a sample such as a light source to be measured, and images composed of the light rays having transmittance wavelength bands of the respective filters are captured by a two-dimensional image sensor disposed on an imaging plane to acquire information relating to two-dimensional spectral characteristics of the sample to be measured.
<Type Using a Dispersed Image through a Slit>
According to a luminance measuring system, an image formed by an objective optical system of a two-dimensional light source, which is an object for measurement, is formed by a slit disposed on an imaging plane. The slit image, namely, a slit light source, is dispersed for each wavelength by a dispersive optical system, and the dispersed images are captured by a two-dimensional image sensor disposed on the imaging plane. Then, the object for measurement or the optical system for measurement is scanned in a direction orthogonal to the slit to acquire information relating to two-dimensional spectral characteristics of the object for measurement.
The system using the multiple filters is advantageous in the aspect of compatibility with a human eye having superior spatial resolution to wavelength resolution. However, in this case, a band pass filter of a size capable of covering the imaging light rays is necessary for each wavelength, and consequently, the size of a mechanism for successively guiding the band pass filters to the optical path of the light rays is increased. On the other hand, according to the system using a dispersed image through a slit, it is necessary to provide a mechanism for scanning the object for measurement or the optical system for measurement with an intended image resolution. In this case, it is necessary to scan the object for measurement or the optical system for measurement with such a spatial resolution that requires a large load. In any case, both of the systems unduly increase the size and the production cost of the spectroradiometer, and also unduly extend the time required for scanning, namely, the time required for measurement.